1. Field of the Invention
The present invention relates to an ink composition, an ink set and an inkjet recording method, and more particularly to technology for accelerating the aggregation reaction speed of an ink composition.
2. Description of the Related Art
An inkjet recording apparatus has been known which carries out recording by ejecting ink droplets respectively from a plurality of nozzles formed in an inkjet head. The inkjet recording apparatus has been widely used due to the low noise during recording, their low running costs, and their ability to record images of high quality on a wide variety of recording media.
Inkjet recording methods have been known which form an image temporarily on an intermediate transfer body by depositing ink droplets onto the intermediate transfer body from an inkjet head, and then transferring the image onto a recording medium. According to this transfer type of recording method, it is possible to remove the ink solvent (for example, water) on the intermediate transfer body by means of a solvent removal roller or other such device, before transferring the image onto the recording medium, and therefore problems, such as image bleeding, print-through, deformation of the recording medium (known as “cockling”), and the like, caused by the presence of the ink solvent, can be avoided, and a high-quality image can be obtained.
Furthermore, a two-liquid reaction method of the inkjet recording methods has been known which causes an ink to react with a treatment liquid for aggregating the ink. In this two-liquid reaction method, the fixing of the ink on the recording medium can be promoted by causing the ink to aggregate by means of the treatment liquid.
If the two-liquid reaction method is applied to a transfer type of inkjet recording method, then in order to achieve a compact size of the inkjet recording apparatus, it is necessary to shorten the time period from the time at which the ink makes contact with the treatment liquid on the intermediate transfer body until the ink aggregates. When the ink makes contact with the treatment liquid, the aggregate of the ink is produced by means of the aggregation reaction. The solvent in the aggregate is then removed when it is conveyed to the solvent removal roller. If the aggregate reaction speed is slow, then the distance from the droplet ejection nozzles until the solvent removal roller must be kept to a long distance, and consequently the inkjet recording apparatus becomes large in size.
Examples of the related art which uses a two-liquid reaction method in a transfer type of inkjet recording method are described in Japanese Patent Application Publication No. 2003-82265 and Japanese Patent Application Publication No. 2004-338361.
Japanese Patent Application Publication No. 2003-82265 describes a method which includes the steps of: mixing together, on a transfer body, a recording liquid containing at least a coloring material, and a treatment liquid containing a reactive component which reacts with at least one reactive component in the recording liquid; and transferring the combined material onto a recording medium. Moreover, it also describes using a recording liquid containing a resin emulsion having an ionic group on at least the surface of the resin particles, as a reactive component in the recording liquid which reacts with the reactive component in the treatment liquid. By this means, when recording at high speed, bleeding does not occur in the image on the transfer body, and a high transfer rate is obtained.
Furthermore, Japanese Patent Application Publication No. 2004-338361 describes using an ink set which includes: a treatment liquid containing particles whose dispersed state is maintained or broken down due to external factors; and a recording liquid containing a coloring material whose dispersed state or dissolved state is maintained or broken down due to external factors. By using this ink set, the dispersed state or the dissolved state of the treatment liquid and the recording liquid can be respectively broken down on the recording medium, and an image is thereby formed by means of the particles in the treatment liquid and the coloring material in the recording liquid aggregating without substantially mixing together. Therefore, it is possible substantially to suppress feathering and color bleeding on both an absorptive or a non-absorptive recording medium, and furthermore, a bright printed object which has high density and color saturation and which is faithful to the original document, can be obtained, as well as applying a luster to the printed object.
However, the ink compositions used in Japanese Patent Application Publication No. 2003-82265 and Japanese Patent Application Publication No. 2004-338361 have drawbacks in that an ink composition and a treatment liquid are ejected from respective nozzles, the aggregation reaction speed from contact on the intermediate transfer body until aggregation is slow, and a long time is required until the solvent can be removed by the solvent removal roller. Consequently, there is a problem in that the inkjet recording apparatus becomes large in size, and it becomes especially large in size in the case of an inkjet recording apparatus which requires fast recording.
Furthermore, if the two-liquid reaction method is used to aggregate directly on the recording medium, without using the intermediate transfer body, if the aggregation reaction speed between the ink composition and the treatment liquid is slow, then the coloring material permeates together with the solvent which permeates into the recording medium, the fixing characteristics on the recording medium deteriorate, and therefore the recording density and color definition decline. Consequently, accelerating the speed of the aggregating reaction between the ink composition and the treatment liquid is a serious issue in a normal inkjet recording method other than a transfer type of method.